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Environmental Factors That Influence Herbicide Performance. Dr. Eric P. Prostko Extension Weed Specialist University of Georgia Tifton. For a herbicide to work it must…. come in contact with a plant surface (root, shoot, leaves)

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environmental factors that influence herbicide performance

Environmental Factors That Influence Herbicide Performance

Dr. Eric P. Prostko

Extension Weed Specialist

University of Georgia

Tifton

for a herbicide to work it must
For a herbicide to work it must…..
  • come in contact with a plant surface (root, shoot, leaves)
  • remain at site long enough to penetrate or be absorbed
  • move to its site of action
specific environmental factors
Specific Environmental Factors
  • soil

* organic matter, texture, CEC, pH

  • climatic

* temperature, moisture, humidity, light intensity, dew(?)

soil factors organic matter and texture
Soil FactorsOrganic Matter and Texture
  • most important for soil applied herbicides
  • Indirectly influences all processes that affect herbicides!!
  • the greater the organic matter and clay content, the greater adsorption of herbicides
amount of atrazine required to reduce the growth of giant foxtail by 50 at varying om levels

5

4.5

4

3.5

3

Rate (kg/ha)

2.5

2

1.5

1

0.5

0

0.8

1.9

3.9

6.4

11

18

OM (%)

Amount of atrazine required to reduce the growth of giant foxtail by 50% at varying OM levels.

Parochetti 1973

soil factors cation exchange capacity cec
Soil FactorsCation Exchange Capacity (CEC)
  • soils ability to adsorb positively charged compounds
  • fine-textured, high-organic matter soils have larger CEC’s than coarse, low-organic matter soils

paraquat

soil factors cation exchange capacity
Soil FactorsCation Exchange Capacity
  • influences rate of application
  • not found on many herbicide labels
soil factors ph
Soil FactorspH
  • influences water solubility, adsorption, and hydrolysis
  • triazines
  • sulfonylureas
  • imidazolinones
effect of ph on adsorption of atrazine

14

12

10

8

Kd Value

6

4

2

0

3.9

4.7

5.3

6

8

pH

Effect of pH on Adsorption of Atrazine

McGlamery and Slife, 1966

slide14
Soil pH may influence rotational restrictions because of its effects on adsorption, solubility, and degradation.
climatic effects temperature
Climatic EffectsTemperature
  • In showy crotalaria, Blazer absorption was 4X greater at 810 and 950 than at 640.(Wills and McWhorter, 1981)
  • In johnsongrass, Roundup absorption doubled as temperature was increased from 750 to 950.(McWhorter et al. 1980)
climatic effects moisture ppi pre
Climatic EffectsMoisture - PPI/PRE
  • activation

* movement

* 0.5” within 7-10 d

  • adsorption

* availability

effect of rainfall amount after application on herbicide performance

0

0.1"

0.25"

0.5"

1"

100

80

60

Foxtail Control (%)

40

20

0

Dual

Frontier

Herbicide

Effect of Rainfall Amount After Application on Herbicide Performance

Simmons et al. 1997

climatic effects moisture post
Climatic EffectsMoisture - POST

Dry weather causes…..

  • plants to develop thicker cuticles
  • reductions in absorption, retention, and translocation
  • altered metabolism
climatic effects relative humidity
Climatic EffectsRelative Humidity
  • Liberty treatment at 95% RH resulted in complete plant death in contrast to only a 30% inhibition in growth at 40% RH(Anderson et al. 1993)
climatic effects relative humidity20
Climatic EffectsRelative Humidity
  • A higher relative humidity level …..

* extends drying period of herbicide droplets.

* hydrates plant cuticles.

climatic effects light intensity
Climatic EffectsLight Intensity
  • influences photosynthesis, cuticle development, stomatal openings, and photodecomposition
climatic effects what about dew
Climatic EffectsWhat about dew?
  • studies have shown that dew can either increase or decrease foliar herbicide efficacy (Caseley 1989)
  • decrease - runoff and dilution
  • increase - cuticle hydration and uptake
effect of volume and dew on roundup efficacy on oats

0

50%

100%

100

80

60

Control - %

40

20

0

16

32

48

Spray Volume (GPA)

Effect of Volume and Dew on Roundup Efficacy on Oats

Dew Level

Kogan and Zuniga, 2001

summary
Summary
  • Environmental factors cannot be controlled (except irrigation).
  • Need to understand environmental effects and make applications when conditions are favorable for optimum performance if possible.
slide25

University of

Georgia

Extension

Weed Science

(gaweed.com)